Date: Thu, 22 Jul 2010 00:20:07 -0400 (EDT) From: Charles Sprickman <spork@bway.net> To: Adam Vande More <amvandemore@gmail.com> Cc: freebsd-stable <freebsd-stable@freebsd.org>, Dan Langille <dan@langille.org> Subject: Re: Using GTP and glabel for ZFS arrays Message-ID: <alpine.OSX.2.00.1007220009210.33454@hotlap.local> In-Reply-To: <AANLkTimbYGpC0aYGnE61J5ZopQVD9m8hrz07CZAnsvsq@mail.gmail.com> References: <4C47B57F.5020309@langille.org> <AANLkTimbYGpC0aYGnE61J5ZopQVD9m8hrz07CZAnsvsq@mail.gmail.com>
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On Wed, 21 Jul 2010, Adam Vande More wrote: > On Wed, Jul 21, 2010 at 10:05 PM, Dan Langille <dan@langille.org> wrote: > >> Why '-b 34'? Randi pointed me to >> http://en.wikipedia.org/wiki/GUID_Partition_Table where it explains what >> the first 33 LBA are used for. It's not for us to use here. >> >> Where SOMEVALUE is the number of blocks to use. I plan not to use all the >> available blocks but leave a few hundred MB free at the end. That'll allow >> for the variance in HDD size. >> >> Any suggestions/comments? Is there any advantage to using the -l option on >> 'gpart add' instead of the glabel above? >> > > You'll want to make sure your partitions are aligned, discussion here(says > 4k drives, but info pertinent to all): > > http://lists.freebsd.org/pipermail/freebsd-hackers/2010-March/031154.html >From that thread: http://lists.freebsd.org/pipermail/freebsd-hackers/2010-March/031173.html (longer explanation) I'm not really understanding the alignment issue myself on a few levels: -Does it only affect the new drives with 4K blocks? -If it does not, is it generally good to start your first partition at 1MB in? How exactly does doing this "fix" the alignment issue? > My understanding is that you weren't booting from zfs, just using it as an > data file system. In that case, you'd want to use "gpart add -b 512 ..." > or some other multiple of 16. Even 1024 would be a good safe number. Also > GPT creates partitions not slices. Your resulting partitions with be > labeled something like ad0p1, ad0p2, etc. I assume the same can be applied if you do boot from zfs; you'd still create the "freebsd-boot" partition starting at 34, but your next partition (be it swap or zfs) would start either 512 or 1024 sectors in? Thanks, Charles > > > -- > Adam Vande More > _______________________________________________ > freebsd-stable@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-stable > To unsubscribe, send any mail to "freebsd-stable-unsubscribe@freebsd.org" >
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